The present invention relates to a novel light sensitive photoresist composition which is used for the photo-engraving process or for production of phosphor screen of color picture tubes.
Light sensitive photoresist compositions which change the solvent solubility under irradiation, are used for precision processing in the photoengraving process or in the production of phosphor screen of color picture tubes.
These light sensitive photoresist compositions are roughly divided in two types, namely the water-insoluble type and the water-soluble type, and these two types are applied properly depending on the intended use.
Water-insoluble light sensitive photoresist compositions require use of organic solvents, and in view of the cost and toxicity, they recently tend to be replaced by water-soluble light sensitive photoresist compositions.
A typical instance of well-known water-soluble light sensitive photoresist compositions is a mixture comprising a water-soluble polymer such as gelatin and polyvinyl alcohol and a dichromate such as ammonium dichromate. This mixture has such a property that it is rendered water-insoluble under irradiation of light. However, this light sensitive photoresist composition undergoes chemical changes at room temperature even under no irradiation, and therefore, it is defective in that the light sensitive characteristics are degraded while it is stored for a long time.
As means for overcoming this defect, it has been proposed to use a diazonium compound or an azide compound instead of the dichromate. Especially, a mixture of a water-soluble polymer and an azide compound is characterized in that it is quite stable in the dark and it can be stored for a long time without degradation of the light sensitive characteristics.
Among such azide compounds that can be used as one component of the light sensitive photoresist composition, a compound represented by the following structural formula I, namely disodium 4,4'-diazidostilbene-2,2'-disulfonate, is especially suitable for use in combination with a water-soluble polymer and is used broadly: ##STR1## When a mixture of this azide compound and a water-soluble polymer is irradiated with rays of a suitable wave length, the azide compound absorbs the light energy and decomposes, and the decomposition product cross-links polymer molecules to render the polymer water-insoluble. This insolubilization reaction is not caused to occur at room temperature unless the mixture is irradiated.
This practical azide compound represented by the structural formula I absorbs intensely rays of a wave length of 300 to 360 nm as shown by Curve I on FIG. 1. Therefore, a light sensitive photoresist composition comprising a mixture of this azide compound and a water-soluble polymer has an especially high sensitivity to rays having a wave length of 300 to 360 nm.
As the light source for light sensitive photoresist compositions, there are generally employed a carbon arc, a tungsten lamp, a super high pressure mercury lamp, a xenon lamp and the like. The light emitted from these light sources include not only rays having a wave length of 300 to 360 nm but also rays having a longer wave length. Accordingly, if these rays having a wave length longer than 360 nm be effectively utilized for the photo-chemical reaction in light sensitive photoresist compositions, it will be possible to increase the sensitivity in the compositions.
As the known azide compound that shows a spectral absorption in a longer wave length region than the azide compound represented by the structural formula I and can be used as a light sensitive component of a light sensitive photoresist composition, there can be mentioned, for example, condensates of an aldehyde such as p-azidobenzaldehyde and p-azidocinnamaldehyde with an aliphatic ketone such as acetone and cyclohexanone. These azide compounds, however, are insoluble in water and therefore, no water-soluble light sensitive photoresist compositions can be obtained by mixing these azide compounds with water-soluble polymers.